As is known, sensors are used to perform various functions in a variety of applications. Some sensors include one or magnetic field sensing elements, such as a Hall effect element or a magnetoresistive element, to sense a magnetic field associated with proximity or motion of an object, such as a ferromagnetic object in the form of a gear or ring magnet, or to sense a current, as examples.
Sensors are often provided in the form of an integrated circuit (IC) containing one or more semiconductor die supporting the sensor electronic circuitry (referred to herein also as functional circuit(s)) and optionally also containing additional elements, such as a magnet and/or passive components, such as capacitors, inductors, or resistors.
Power can be supplied to sensor integrated circuits through one or more pins from an external supply, such as from a car battery. The sensor output signal(s) are sometimes provided through one or more dedicated output pins. Alternatively, some sensors encode an output in the form of a current signal on the power and ground connections. Such sensors are sometimes referred to as “two-wire” devices and advantageously have fewer pins.
Power from the external power supply can experience various disturbances that can adversely impact a sensor's ability to provide accurate output information. Power disturbances include, for example, interruptions and transients due to intermittent connections, short circuits, open circuits, and/or coupled transients.
Sensor integrated circuits are widely used in automobile control systems and other safety critical applications. It is increasingly important for sensor ICs to function properly even in the presence of power disturbances to the extent possible. Preferably, the sensor IC can withstand some level of power disturbances while still providing an accurate output.
One approach to address this problem has been to use a supply line filter, such as a resistor capacitor (RC) filter, that functions to both filter transient disturbances and store energy to power the IC during a power interruption. However, this approach is limited by the size of the passive components, as well as the degradation of supply bandwidth that can be tolerated in the case of a two-wire sensor that communicates its output through the supply lines.
Some sensors contain reset circuitry that causes the sensor, or certain portions of the sensor, to shut down if power to the IC experiences a disturbance of a certain severity (e.g., magnitude and/or duration). If operational interruption is unavoidable due to the extent of the disturbance, then it is important for the IC to restart in the proper state.